EP0196477B1

EP0196477B1 - Driving status discrimination device for a motor vehicle

Info

Publication number: EP0196477B1
Application number: EP86102814A
Authority: EP
Inventors: Kunihiko Eto; Yutaka Mori; Shigeo Tanooka; Akihiro Ohno
Original assignee: Toyoda Koki KK
Current assignee: Toyoda Koki KK
Priority date: 1985-03-27
Filing date: 1986-03-04
Publication date: 1989-07-26
Also published as: KR950015023B1; DE3664604D1; EP0196477A1; KR860007120A; US4747055A

Description

The present invention relates to a driving status discrimination device in accordance with the prior art portion of claim 1.
DE-A-3 424 826 discloses a driving status discrimination device of the above mentioned type. The prior art device is provided with a steering angle detection means for detecting the steering angle of a steering wheel and with a vehicle speed detection means for detecting the actual vehicle speed and processing means for processing both the steering angle signal detected at a predetermined interval from the steering angle detection means and a speed signal as generated by the vehicle speed detection means. The judging means determine the kind of road on which the vehicle is travelling from the processing result of the processing means and varies the rotational speed of the pump of the servosteering system based on the processing result. It appears to be a drawback of this prior art driving status discrimination device that a discrimination on the mere basis of a vehicle speed signal and a steering frequency signal does not allow a sufficiently reliable judgement as to whether the vehicle is travelling on a mountain road or on a town street. Accordingly, the degree of servoassistance provided by this prior art servosteering system is not always perfectly matched to the actual kind of road.
Generally, in a known prior art power steering device as disclosed in, for example JP-A 58 209 655, the vehicle speed, the steering angle and the steering angle velocity are detected so as to vary the mechanical resistance against its rotation, depending on these parameters. In other words, the steering is made light during low speed running and heavy during a high speed running.
In view of this prior art, the present invention is based on the object of providing a driving status discrimination device of the above mentioned type, capable of automatically and reliably judging the ve- hide driving status.
This object is achieved by a driving status discrimination device in accordance with the prior art portion of claim 1, having the features indicated in the characterising portion thereof.
The driving status discrimination device, in accordance with claim 1, utilises a data analytical tool in statistics for reliable judgement of the vehicle driving status.
The rotational position of the steering wheel is analysed each time the vehicle runs for a predetermined time period or through a predetermined driving distance. Considering rotations of a steering wheel in a statistical viewpoint, a town street driving requires small angle rotations at a large frequency and large angle rotations at not a small frequency. On the other hand, a mountain road driving requires medium angle rotations at a large frequency due to many curves and samll and large angle rotations at smaller frequencies than those in the town street driving. Accordingly, the discrimination of the mountain road driving from the town street driving can be reliably effected through such an analysis of the steering wheel rotation.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The foregoing and other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiments, wherein like reference numerals designate identical or corresponding parts throughout the several views, and in which:

FIGURE 1 is a block diagram of a power steering system to which a driving status discrimination device according to the present invention is applied;
FIGURE 2 is a fragmentary sectional view of a fluid bypass mechanism incorporated into a power cylinder 12 shown in FIGURE 1;
FIGURE 3 is a fragmentary sectional view of a flow control mechanism incorporated into a pump 15 shown in Figure 1;
Figure 4 is graphs showing variations in electric currents applied to solenoid valves of the mechanisms shown in Figures 2 and 3;
Figure 5 (a) is a data table showing values corresponding to steering angles which are actually measured at an interval of 10 meter run during a mountain road drifing;
Figures 5 (b) and 5 (c) are histograms showing the distributions of absolute and real values of the values shown in Figure 5 (a);
Figure 6 (a) is a data table showing values corresponding to steering angles which are actually measured at an interval of 10 meter run during a town street drifing;
Figures 6 (b) and 6 (c) are histograms showing the distributions of the absolute and real values of the values shown in Figure 6 (a);
Figure 7 is a flow chart of a driving status discrimination program executed by a microprocessor 51 shown in Figure 1;
Figure 8 is a flow chart of a solenoid drive control program executed by the microprocessor 51; and

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and particularly to Figure 1 thereof, a power steering device 10 is composed of a servovalve 11 and a power cylinder 12. The servovalve 11 is coupled to a steering wheel 18 through a steering column 18a, while the power cylinder 12 is coupled to steerable wheels (not shown) through link mechanisms (not shown). As well known in the art, when a manual steering torque is applied to the steering wheel 18, an output steering torque increased by the power cylinder 12 is transmitted to the steerable wheels. The steering device 10 is supplied with pressurized fluid from a pump 15 which is drivingly connected to an automotive engine (not shown) through a driving belt 17.
A solenoid valve 20 is provided for controlling the bypass fluid communication between opposite chambers of the power cylinder 12 which are selec-
tively supplied with pressurized fluid from the pump 15 through the servovalve 11, so as to control an assisting power generated by the power cylinder 12. As shown in Figure 2 in detail, the valve 20 is provided with a spool 23, which is slidably received in a hole 22 of a valve body 21, and a solenoid 24. The spool 23 is normally held by a spring 25 at its lower stroke end to discontinue the communication of passages 26, 27 which respectively lead to the opposite chambers of the power cylinder 12. However, when the solenoid 24 is energized to attract the spool 23, the spool 23 is displaced upwardly against the force of the spring 25, so that the passages 26, 27 communicate with each other through a bypass slit 28.
As illustrated in FIGURE 3, a flow control valve 30 for controlling the exhaust volume of the pump 15 is composed of a solenoid valve 31 for adjusting the opening degree of a throttle 39, and a valve spool 35 which slides in response to the pressure difference across the throttle 39 to open and close a bypass hole 38 for controlling pressurized fluid which is supplied from an outlet hole 36 to the servovalve 11 through a delivery port 37. The solenoid valve 31 is provided with a movable spool 32, integrally connected with a valve rod 32a, and a solenoid 33. The movable spool 32 is normally urged by a spring 34 toward the left as viewed in FIGURE 3 to fully open the throttle 39. However, as the energization of the solenoid 33 causes the movable spool 32 to be displaced towards the right against the spring 34, the valve rod 32a approaches the throttle 39 to decrease the opening degree, and thus, the valve spool 35 is moved to decrease the volume of pressurized fluid supplied to the servovalve 11.
Referring back to FIGURE 1, a reference numeral 50 denotes an electronic controller. This controller 50 is primarily composed of a microprocessor 51, a random access memory (hereafter referred to as "RAM") 52, and a read-only memory (hereafter. referred to as "ROM") 53. The microprocessor 51 is coupled through an interface 60 to solenoid drive circuits 61, 62 for controlling electric currents (iB, iA) applied to the solenoids 24, 33 of the solenoid valves 20, 31. The microprocessor 51 is also coupled to a steering angle sensor 40 through an interface 47 and a phase discrimination circuit 45. The steering angle sensor 40 comprises a rotary disc 41 secured to the steering column 18a and two photo interrupters 42, 43 and detects the steering angle (es) based upon the signals from the photo interrupters 42, 43. Further, the microprocessor 51 is coupled to a vehicle speed sensor 46 through the interface 47. The vehicle speed sensor 46 may be composed of a tachometer, which is drivingly connected to an output shaft of a transmission mechanism (not shown) for detecting the vehicle speed based upon the frequency at which pulse signals are generated by the vehicle speed sensor 46.
The ROM 53 stores in the form of characteristic maps control patterns each defining electric currents (iB, iA) applied to the solenoids 24, 33 of the solenoid valves 20, 31. As shown in FIGURE 4, the control patterns include a control pattern I which is a combination of characteristic maps IA, IB for use in mountain road driving and another control pattern II which is a combination of characteristic maps IIA, IIB for use in town street driving. The characteristic maps IA, IIA are used for driving the solenoid 33 of the flow control valve 30, while the characteristic maps IB, IIB are used for driving the solenoid 24 of the solenoid valve 20.
In the control pattern I for the mountain road driving, the characteristic according to which the electric current (iB) to be applied to the solenoid 24 varies relative to a value or parameter (V) corresponding to the vehicle speed and the characteristic according to which the electric current (iA) to be applied to the solenoid 33 varies relative to another parameter (e) corresponding to the steering angle are each set to be increased at a substantially constant rate, as indicated in the characteristic maps IB, IA. Thus, according to the control pattern I, a required manual steering torque becomes large gradually with increases in the vehicle speed as well as in the steering angle. It is to be noted that the gradients in the characteristic maps IB, IA are determined so that the required manual steering torque is moderately increased to enable the vehicle driver to feel the load resistance. This prevents the steering wheel from being excessively turned in the mountain road driving to thereby ensure a stable steering feeling transmitted to the vehicle driver.
On the other hand, in the control pattern II for the town street driving, the variation characteristic of the electric current (iB) relative to the parameter (V) is set to be almost the same as that in the characteristic map IB, as indicated in the characteristic map IIB, while the variation characteristic of the electric current (iA) relative to the parameter (e) is set to have a smaller gradient than that in the characteristic map IA, as indicated in the characteristic map IIA. Accordingly, in the town street driving, the required manual steering torque becomes large with increases in the vehicle speed at the same rate as in the case of the mountain road driving, but it does not become large with increases in the steering angle to the extent that it corresponds to values in the mountain road driving, so that the characteristic is appropriate to the town street driving during which the steering wheel is frequently turned within large angles.
The RAM 52 has a storage area for storing a predetermined number of parameters (e) each corresponding to a steering angle (es). The ROM 53 stores a driving status discrimination program, which enables the microprocessor 51 to store parameters (e), corresponding to steering angles (es) detected by the steering angle sensor 40, one after another in the RAM 52 at a predetermined time interval for renewal purpose, and to count the frequency of parameters (e) other than those within center and opposite end intervals as classified in the form of a histogram. The program further enables the microprocessor 51 to calculate an index (J) representative of the driving status (hereafter referred to as "mountain road index") based upon the counted frequency and all of the stored parameters (e), to make a judgement of whether the vehicle is in the town street driving status or in the mountain road driving status, and to select based upon the result of such a judgement the control patterns I, II for the electric currents (iA), (iB) to be applied to the solenoid valves 31, 20.
FIGURES 5(c) and 6(c) show frequency distribution of the parameters (e) which correspond to steering angles (es) as actually detected. In mountain road driving, the frequency distribution occurs as shown in FIGURE 5(c) because of many curve turns and few right-angle turns. In town street driving, on the other hand, the frequency distribution occurs as shown in FIGURE 6(c) because of few curve turns and not few right-angle turns at intersections. Consequently, the mountain road index (J) calculated in the mid curse of the execution of the discrimination program indicates a larger value in the mountain road driving than that in the town street driving. The further execution of the discrimination program permits the vehicle driving status to be automatically judged, and either of the control patterns I, II shown in FIGURE 4 can be selected based upon the result of such judgement.
During the vehicle driving, the steering angle signal which momentarily varies is detected by the steering angle sensor 40 as a parameter (e) corresponding to the steering angle (es). The steering angle signal is input to a counter (not shown) through the phase discrimination circuit 45. The parameter (V) corresponding to a vehicle speed (Vs) detected by the vehicle speed sensor 46 is input to another counter (not shown) as well.
The microprocessor 51 executes processing operations according to the discrimination program shown in FIGURE 7 in response to an interrupt signal input thereto each time a predetermined driving distance is reached. First of all, a steering angle parameter (0) stored in the counter is read in step 100, and a count value (n) in a sampling number counter (not shown) is compared with a set value (N) in step 101. As the sampling number right after the driving start is small to satisfy n < N, the routine is advanced to step 102 to add "1" to the sampling number count value (n), and the absolute value of the parameter (e) is stored in an n-th address Mn of the storage area of the RAM 52.
When the sampling number (n) increases to reach the set value (N), the routine is directed from step 101 to step 104, wherein the stored content is refreshed or renewed in such a manner as to shift in turn a value at address M2 to address M1 a value at address M3 to address M2......., and finally, to store the absolute value of the newest (n-th) value (e) to the last address Mn. In this situation, the sampling number count value remains to indicate n (=N).
Step 103 and step 104 are followed by step 105, in which a read-out counter (H) is set with the sampling number count value (n), and the comparison of the value(MH) at the N-th address with two set values (B and C) is made in step 106. These set values (B and C) are respectively a slightly larger value than a center interval (a) value (i.e., zero) of the stored parameters (e) corresponding to steering angles (es) and a smaller value than the absolute value of the value in the opposite end intervals (y). In an example wherein actually measured values (e) are shown in FIGURES 6(a) and 7(a), it is determined to be B=3 and C=12. Directly unless B ≤ MH ≤ C holds in step 106 or after the addition of "1" to the value (D) (which is reset each time the discrimination program is executed) of the frequency counter in step 107 if B a MH ≤ C holds in step 106, step 108 follows to subtract "1" from the value (H) of the read-out counter. In step 109, the value (H) of the read-out counter is compared with a numeral "0", and the above-noted steps 106-108 are repeatedly executed until the value (H) becomes 0 (zero), so as to move to step 110 upon the confirmation of H = 0. Consequently, when H = 0 holds, the value (D) in the frequency counter indicates the number of stored values (Mn) each satisfying B a Mn ≤ C.
Step 110 is executed to calculate the mountain road index (J) based upon the following equation. J=D/n Ascertainment is subsequently made in step 111 as to whether the mountain road index (J) is larger than a reference value (E) or not. When J > E is ascertained, the values (e) have a distribution shown in FIGURE 5(b) to represent the mountain road driving. On the other hand, when J > E is not ascertained, the values (e) have another distrubution shown in FIGURE 6(b) to represent the town street driving. A driving status flag F is set with "1" in step 112 unless J a E holds, while it is set with "0" in step 113 if J ≤ E holds. The reference value(E)is predetermined based upon the distribution of the values (e) in each driving status. In the illustrated instance having values (e) exemplified as referred to later, the reference value (E) is set to be 0.3.
The equation in step 110 may be J = D / N. In this modified case, a smaller sampling number (n) makes the mountain road index (J) smaller, so that the driving right after the driving start is judged to be a town street driving. However, as the sampling number (n) comes close to the value (N), it becomes possible to judge the actual driving status correctly. This modification is useful to avoid that too many changes in the state of the driving status flag F is caused right after the driving start due to a fewer number of sampling times.
Upon completion of either of steps 112 and 113, the microprocessor 51 halts the execution of the routine shown in FIGURE 7 until it receives the next interrupt signal and instead, begins to execute a solenoid drive control program shown in FIGURE 8 as follows:
First of all, step 200 is executed to read values (V) and (e) which are stored in the respective counters to represent the vehicle speed (Vs) and the steering angle (es), and step 201 is then reached to read the state of the driving status flag F. In subsequent step 202, the value in the driving status flag F is ascertained, wherein unless F = 1, the processing is advanced to steps 203 and 204, so that the characteristic maps IA, IB for mountain road driving in the ROM 53 are searched based upon the read values (e) and (V) for electric currents (iA, iB) so as to apply the same respectively to the solenoids 33, 24 of the solenoid valves 31, 20. If F = 1 in step 202, steps 205 and 206 then follow, so that the characteristic maps IIA, IIB for town street driving in the ROM 53 are searched by reference to the read values (e) and (V) for electric currents (iA, iB) so as to apply the same to the solenoids 33 and 24 of the solenoid valves 31, 20. Upon completion either of steps 204 and 206, the microprocessor 51 halts the execution of the routine shown in FIGURE 8.
In this manner, the microprocessor 51 executes the above-described programs in response to an interruption signal which is generated each time the vehicle runs a predetermined distance, whereby the assisting power is set depending upon the driving status.
FIGURES 5(a) and 6(a) indicate actual data (the number of samplings: 130) which the microprocessor 51 detected in response to an interruption signal input thereto each time the vehicle ran ten (10) meters during a mountain road driving and a town street driving. Each value (e) of the actual data represents one-eighteenth (1/18) a steering angle (es) of the steering column 18a when the vehicle reaches a point represented by a cumulative distance C + D (scale: 10 meters). FIGURES 5(c) and 6(c) respectively show histograms in each of which actual values (e) in each of FIGURES 5(a) and 6(a) are classified at the interval of five (5) degrees, while FIGURES 5(b) and 6(b) respectively show histograms in each of which absolute values of the actual values (e) are classified at the interval of five (5) degrees.
The comparison of each histogram with a corresponding one makes the following clear. That is, in a mountain road driving involving many curve runs and few right-angle turns, the frequency of steering turns is relatively large within a medium steering angle interval (p), but is extremely small within a large steering angle interval (y), compared with the frequency of steering turns in a small steering angle interval (a), as shown in FIGURES 5(b) and 5(c). On the contrary, in a town street driving involving few curve turns and relatively many right-angle turns at intersections, the frequency of steering turns is extremely large within the small steering angle interval (a) and small within the large steering angle intervals (y) as well as within the medium steering angle interval (p). The mountain road driving and the town street driving provide for a distinct difference therebetween in the frequency distribution in the values (e) as mentioned above.
Accordingly, the above-noted mountain road index (J) is calculated by counting the frequency of the values (e) which do not include those classified within the narrow interval (a) and those classified within wide intervals (y) and by dividing the counted frequency by all the number (N) of the values (e). Herein, the interval (a) makes a center interval to satisfy a relation -B < ₆ < B, while the intervals (y) make opposite end intervals to satisfy relations e < -C and C < e. In the illustrated example, boundary values (B) and (C) are "3" and "12" respectively, and the frequency (D) and the mountain road index (J) respectively have values shown in the following TABLE 1 wherein standard deviations (a) calculated from the values (e) indicated in FIGURES 5(b) and 6(b) are also recited for comparision.
The difference (ratio: 3.90) between the mountain road driving and the town street driving in the mountain road index J is larger than the difference (the ratio: 1.12) therebetween in the standard deviation (a). Therefore, the discrimination of driving status can be reliably effected by reference to the mountain road index (J). In this case, it is proper to set "0.3" as the reference value (E) for the discrimination.
The calculation for the mountain road index (J) can also be made utilizing histograms of real figures of the values (e) shown in FIGURES 5(c) and 6(c), although the aforementioned flow chart shown in FIGURE 7 is provided for calculating the mountain road index (J), utilizing the absolute values of the values (e).
A second embodiment of the present invention will be described hereafter. In this embodiment, for discrimination of the mountain road driving from the town street driving, a mean value (X) of the absolute values which are distributed as shown in Figures 5 (b) and 6 (b) is used instead of the above-noted mountain road index (J) as used in the foregoing first embodiment.
The following Table 2 shows the mean values (X) and a standard deviations (a) of absolute values of the values (e) exemplified in Figures 5 (a) and 6 (a).
The difference (the ratio: 1.61) in the mean value (X) between the mountain road driving and the town street driving is larger than the difference (the ratio: 1.12) in the standard deviation (a) therebetween, and therefore, the discrimination of the driving status can be reliably effected utilizing the mean value (X). In this case, it is proper to determine the reference value (K) to be "3". Although the mean values (X) of the mountain road driving and the town street driving are opposite in a large-small relation to the standard deviations (a) thereof, such is due to the fact that the frequency of steering turns within a large angle is larger in the town street driving than that in the mountain road driving.
Although the above-described embodiments are applied to the steering power control in a power steering device, the present invention may be applied for the height control of a vehicle, the rigidity control of suspension mechanisms or the like.
Although each of the above-described embodiments makes the discrimination by reference to one reference value (E) or (K), there may be set a plurality of such reference values (E) or (K) at suitable intervals. In such a modified case, a plurality of characteristic maps may be prepared for respective intervals divided by the reference values (E) or (K) and may be selected depending upon the value of the mountain road index (J) or the mean value (X). This modification is useful to avoid an abrupt change-over from a mountain road characteristic map to a town street characteristic map.
Further, although the above-described first embodiment uses the mountain road index (J) which is calculated by dividing the frequency (D) of values (e) classified in the intervals (p) by the frequency (N) of all the stored values (e), a reciprocal of the mountain road index (J) may be used as such a mountain road index. Moreover, the discrimination in each of the above-described embodiments may be effected by comparing the reference value (E) or (K) with a modified value to which the mountain road index (J) or the mean value (X) is modified through a suitable calculation (e.g., division by the standard deviation (a)), rather than by directly comparing the mountain road value (J) or the mean value (X) with the boundary value (E) or (K).

Claims

1. A driving status discrimination device provided with steering angle detection means (41, 45) for detecting the steering angle of a steering wheel manually rotatable by a driver of a moter vehicle, processing means (50; 106, 107, 110) for processing steering angle signals (e) detected at a predetermined interval from the steering angle detection means, and judgement means (111-113) for discriminating several kinds of roads on which the motor vehicle is travelling from one another, based on the processing result of the processing means (50; 106, 107, 110) characterized in that the processing means (50; 106, 107, 110) classifies each of the steering angle signals (e) into either of first and second class signals, wherein the value of each first class signal belongs to either of relatively narrow interval (a) including a center value (-2 to 2) of the steering angle signals (e) and other invervals (y) than a relatively wide interval (a+p) including the center value (-2 to 2), while the second class signals are the remainders of the plurality of steering angle signals (e), that the processing means (50; 106, 107, 110) calculates an index value (J) representing the driving status of the vehicle, based upon the second class signals and all of the steering angle signals (₉) output from the steering angle detection means (40, 45), and that in response to the index value (J), judgement means (111-113) discriminates several kinds of road drivings from one another for selectively outputting several road discrimination signets (F=0, F=1).

2. A driving status discrimination device as set forth in claim 1, characterized in that first counter means (102) is further provided for counting the number (n) of the steering angle signals (e) detected from the steering angle detection means (40, 45) and that the processing means (50; 106, 107, 110) in- dudes second counter means (107) for counting the number (D) of the second class signals and division means (110) for calculating the index value (J) by effecting a division between the number (D) of the second class signals counted by the second counter means (107) and the number (n) of the steering angle signals (₀) counted by the first counter means (102).

3. A driving status discrimination device as set forth in claim 1 or 2, characterized in that there is further provided data storage means (52) which has a predetermined number (N) of storage locations for storing the steering angle signals (e) wherein the date storage means (52) is capable of deleting the oldest one of the steering angle signals (θ) each time it receives a new steering angle signal (θ) after the steering angle signals (e) stored therein reaches the predetermined number (N), and that the processing means (106, 107, 110) includes counter means (107), for counting the number (D) of the second class signals and division means (110) for dividing the number (D) of the second class signals counted by the counter means (107), by the predetermined number (N) of the storage locations.

4. A driving status discrimination device as set forth in claim 1, 2 or 3, characterized in that the judgement means (111-113) is composed of comparison means (111) for comparing the index value (J) with a predetermined reference value (E) so as to output a first road discrimination signal (F=0) when the index value (J) is larger than the predetermined reference value (E) and so as to output a second road discrimination signal (F=1) when the index value (J) is smaller than the predetermined reference value (E).